Muscular system in blender
Do you need muscle jiggle? Thats the real question.

If yes you have to use softbody simulation. The Muscle Tools plugin is imho not very helpful, because it treats the muscles one by one and not like a whole muscular system. Here is how I would setup that: 

How do you assign multiple shrinkwrap modifiers to rig muscles?.

If you don't need muscle jiggle than the simulation and shrinkwrap is just overcomplication and you can use bones and shapekeys to do everything. In that regard you can also use stretch maps and lattices for skin sliding.